1. Field of the Invention
Apparatuses consistent with the present invention relate to a pressure control valve.
2. Description of the Related Art
Conventionally, in an oil pressure circuit of an automatic transmission for example, the oil pressure generated by an oil pump has been regulated by a regulator valve so as to be regulator pressure, and the regulator pressure has been supplied to each portion of the oil pressure circuit. Moreover, various types of pressure control valves are disposed in the oil pressure circuit, such as a linear solenoid valve that includes a linear solenoid portion and a regulating pressure valve unit that receives modulator pressure which is obtained by a modulator valve depressurizing the regulator pressure, as input pressure, and actuates the regulating pressure control valve by supplying a current to a coil of the linear solenoid portion so as to regulate the oil pressure, and generates the regulated oil pressure as output pressure.
FIG. 2 is a diagram illustrating principal components of a conventional oil pressure circuit. In the drawing, reference symbol C denotes a clutch as a friction engagement element, and reference numeral 91 denotes a linear solenoid valve including a linear solenoid portion 92 and a regulating pressure valve unit 93. The linear solenoid valve 91 receives the modulator pressure which is obtained by a modulator valve 94 depressurizing the regulator pressure which is regulated by an unshown regulator valve, as input pressure, actuates the regulating pressure valve unit 93 by supplying a current from a control device 95 to an unshown coil of the linear solenoid portion 92, so as to regulate oil pressure, and generates the regulated oil pressure as output pressure.
A control valve 96 receives the oil pressure which is generated by a oil pump 97 as input pressure (original pressure), and also receives the output pressure which is transmitted from the linear solenoid valve 91, as signal oil pressure, generates control pressure, and supplies the control pressure to an unshown oil servo of the clutch C. In this case, the control pressure is supplied to the oil servo in a predetermined oil pressure pattern, and the clutch C is engaged or disengaged based on the oil pressure pattern (for example, see Japanese Examined Patent Application Publication No. 2003-74733). Note that an arrangement may be made wherein a brake is employed as the friction engagement element instead of the clutch C, and the brake is engaged or disengaged based on the oil pressure pattern of the control pressure.
However, in the conventional oil pressure circuit, the linear solenoid valve 91 and the control valve 96 are required for generating control pressure, resulting in not only increasing the number of parts but also complicating the oil pressure circuit.
Consequently, while there is the possibility that control pressure is generated by the linear solenoid valve 91 alone, in this case, when obtaining the control pressure with the maximal oil pressure which is required for engaging with the clutch C, the value of a current supplied to the coil sometimes varies, and consequently, the control pressure cannot be generated in a stable manner.
Great thrust is required in the linear solenoid portion in order to increase the control pressure, and accordingly, the linear solenoid portion 92 is increased in size so as to obtain the great thrust, and consequently, the linear solenoid valve 91 is also increased in size.